Two members of an Islamist organization claimed responsibility in a new video for the deadly bombings in Russia earlier this month, and warned that a “surprise” was in store for the Winter Olympics in Sochi.

The pair of Russian-speaking men from the militant group Vilayat Dagestan said in the video that emerged Sunday that more violence is coming if Russian President Vladimir Putin doesn’t call off the winter games, the Associated Press reports. “If you hold these Olympics, we will give you a present for the innocent Muslim blood being spilled all around the world: in Afghanistan, in Somalia, in Syria,” they say. “For the tourists who come, there will be a present, too.”

The authenticity of the 49-minute video, which shows the pair of men appearing to construct explosive devices and explain why they would attack, could not be verified. The video claims that the duo, identified as Suleiman and Abdurakhaman, were the suicide attackers in deadly blasts earlier this month in the Russian city of Volgograd.

They continued that the two-day Volgograd attack, which killed 34 people over two days, “is only a little example” of what they can do and, in a portion of the video directed at Russian officials, said they “will continue to kill you and your soldiers.”

Putin immediately stepped up security ahead of the Olympics, which take place between Feb. 7-23. Over the weekend, he said he “will try to make sure that the security measures taken aren’t too intrusive or visible and that they won’t put pressure on the athletes, guests and journalists,” but that “at the same time, we will do our best to ensure that these measures are efficient.”